unit 6

A voltage regulator, usually built into the alternator, controls the voltage and current output of the alternator... VOLTAGE REGULATIONThe output from an AC generator can reach as high a

ENGLISH FOR AUTOMOBILE

INDUSTRY

MASTER VO ANH TUAN

UNIT 5: Electronics system

Ignition system

The ignition system is used

on gasoline engines to start

combustion The spark plug

must fire at the correct time

during the compression

stroke A crankshaft position

sensor or a distributor

operates the ignition module

The module operates the

ignition coil The coil

produces high voltage for the

spark plugs

Starting System

The starting system has a powerful

electric starting motor that rotates the

engine crankshaft until the engine “fires” and runs on its own power

A battery provides the electricity for the

starting system When the key is turned to the start position, current flows through the starting system circuit The starting motor is

energized, and the starting motor pinion

gear engages a gear on the engine flywheel

This spins the crankshaft As soon as the engine starts, the driver must shut off the starting system by releasing the ignition key

Charging System

The charging system is needed to replace electrical energy drawn from the battery during starting system operation To re-energize the battery, the charging system forces electric current back into the battery.

When the engine is running, a drive belt spins the alternator pulley The alternator generator) can then produce electricity to recharge the battery and operate other electrical needs of the vehicle A voltage regulator, usually built into the alternator, controls the voltage and current output of the alternator.

The starter circuit

 All the components are earthed to the metal car body Only one wire

is needed to carry current to each component.

Pre-engaged starter

The pinion is moved by

the solenoid; there is an

initial period in which the

motor turns slowly to allow

engagement, so the whole

operation is more gentle

and causes less wear on

the teeth.

Inertia system

 An inertia type starter: this one is an 'inboard' type in which the Bendix gear throws the pinion towards the motor; there are also 'outboard' ones in which it moves the other way.

 The inertia of the heavy piston assembly prevents it from spinning immediately when the motor shaft turns, so it slides along the thread and into engagement; when the engine starts, the pinion is turned faster than its shaft, so it is thrown back out of engagement.

The location of the starter motor brushes and commutator

DC generators had a very limited current output, especially at low speeds

They could not keep up with demands of the modern automobile and were

replaced by AC generators AC generators are capable of providing high

current output even at low engine speeds

AC generators use a design that is basically the reverse of a DC generator

In an AC generator, a spinning magnetic field (called the rotor) rotates inside

an assembly of stationary conductors (called the stator) As the spinning north and south poles of the magnetic field pass the conductors, they induce a

voltage that first flows in one direction and then in the opposite direction (AC voltage) Because automobiles use DC voltage, the AC must be changed or

rectified into DC This is done through an arrangement of diodes that are

placed between the output of the windings and the output of the AC generator

 The voltage regulator adjusts the generator’s output according to the voltage on the sensing circuit.

VOLTAGE REGULATION

The output from an AC generator can reach as high as 250 volts if it is not controlled The battery and the electrical system must be protected from this excessive voltage Therefore, charging systems use a voltage regulator to

control the generator’s output Voltage output is controlled by the voltage

regulator as it varies the strength of the magnetic field in the rotor Current

output does not need to be controlled because an AC generator naturally

limits the current output To ensure that the battery stays fully charged, most regulators are set for a system voltage between 14.5 and 15.5 volts

Voltage output is controlled by varying the field current through the rotor

The higher the field current, the higher the voltage output By controlling the

amount of resistance in series with the field coil, control of the field current

and voltage output is obtained

Distributor ignition

The ignition switch is usually mounted on the steering

column or dashboard, and controls the flow of current between

the battery and ignition system.

The battery is the source of electric power when the engine

is stationary It also supplements the power from the generator

when it is not turning fast enough to produce 12 volts.

The distributor directs the flow of high-tension current from the coil through the rotor arm, and distributes it to each spark

plug in turn The distributor is usually driven direct from the

camshaft and is geared to turn at half engine speed.

The HT current from the distributor passes down the central

core of the spark plug, then produces a spark as it jumps the gap to the side electrode.

The coil consists of a metal casing containing two sets of

insulated wire windings on a soft-iron central core The collapse

of the magnetic fields generated around the primary windings

produces the HT current in the secondary winding which goes through the distributor to the sparkplugs.

Electronic ignition (EI) Systems

EI systems have no distributor; spark distribution is controlled by an electronic control unit and/or the vehicle’s computer Instead of a single

ignition coil for all cylinders, each cylinder may have its own ignition coil, or two cylinders may share one coil The coils are wired directly to the spark

plug they control An ignition control module, tied into the vehicle’s

computer control system, controls the firing order and the spark timing and advance

The energy produced by the secondary winding is voltage This voltage

is used to establish a complete circuit so current can flow The excess energy is used to maintain the current flow across the spark plug’s gap Distributor-less ignition systems are capable of producing much higher energy than conventional ignition systems